1. Field of the Invention
The present invention relates to erecting equal-magnification lens array plates used in image reading devices and to optical scanning units and image reading devices using the erecting equal-magnification lens array plate.
2. Description of the Related Art
Some image reading devices such as scanners are known to use erecting equal-magnification optics. Erecting equal-magnification optics are capable of reducing the size of devices better than reduction optics. In the case of image reading devices, an erecting equal-magnification optical system comprises a line light source, an erecting equal-magnification lens array, and a line image sensor.
A rod lens array capable of forming an erect equal-magnification image is used as an erecting equal-magnification lens array in an erecting equal-magnification optical system. Normally, a rod lens array comprises an arrangement of rod lenses in the longitudinal direction (main scanning direction of the image reading device) of the lens array. By increasing the number of columns of rod lenses, the proportion of light transmitted is improved and unevenness in the amount of light transmitted is reduced. Due to price concerns, it is common to use one or two columns of rod lenses in a rod lens array.
Meanwhile, an erecting equal-magnification lens array plate could be formed as a stack of a plurality of transparent lens array plates built such that the optical axes of individual convex lenses are aligned, where each transparent lens array plate includes a systematic arrangement of micro-convex lenses on one or both surfaces of the plate. Since an erecting equal-magnification lens array plate such as this can be formed by, for example, injection molding, erecting equal-magnification lens arrays in a plurality of columns can be manufactured at a relatively low cost.
An erecting equal-magnification lens array plate lacks a wall for beam separation between adjacent lenses. Therefore, there is a problem of stray light wherein a light beam diagonally incident on an erecting equal-magnification lens array plate travels diagonally inside the plate and enters an adjacent convex lens, creating noise (also referred to as ghost noise) as it leaves the plate.
Some devices are known to address stray light, which does not contribute to imaging, by forming a light shielding wall on an erecting equal-magnification lens array plate or providing a light shielding member between erecting equal-magnification lens array plates (see patent document No. 1).    [patent document No. 1] JP 2009-069801
However, due to an error in manufacturing members of an erecting equal-magnification lens array plate or an error in assembling the members, light may reach a portion that is not expected to receive light according to the design, and the light reflected or refracted at that portion may cause flare noise. In the presence of flare noise, white flare occurs across an image, resulting in poor S/N ratio.